Abstract 1. 1. Dissociation of prototoxin and activated 12-S toxin of Clostridium botulinum type E under alkaline conditions may occur in two steps: molecular unfolding and molecular division. The molecular unfolding reduces the sedimentation coefficient from 11.6 S to 10.3 S; the molecular division produces the toxic Eα and nontoxic Eβ components of 7.3 S. 2. 2. The Eα and Eβ components of prototoxin or activated 12-S toxin associate at pH 6.0 at an equimolecular ratio to reconstitute toxin molecules of 12 S. Eα of activated 12-S toxin and Eβ of prototoxin also associate. Either component of type-E prototoxin and the counterpart component of type-A toxin do not. The original and the reconstituted activated 12-S toxins showed a similar stability at pH 3.0 and 33°. The reconstituted 12-S toxins mostly underwent molecular division when exposed to pH 7.0, while the original ones only underwent molecular unfolding. 3. 3. The molecule of RNA-prototoxin ∗ of 15.5–16.5 S consists of RNA-proto-Eα ∗ of 12–13 S and proto-Eβ ∗ of 7.3 S at an equimolecular ratio. RNA-proto-Eα and RNA-proto-Eβ also associate.